Alienware M17x R3 Hard Drive Issues-Please Help!

I bought an Alienware M17x R3 February of 2012, and so far it's had minor problems which my Dad and I could easy fix without a problem. Yet lately, the computer has had a couple of problems (not sure if they're linked, I'll leave that up to you) which we I can't seem to find a solution for. Tonight I'll be using my last card, but I doubt that will work. Thus, before I head down to the shop, I'll try to ask you guys. I'm not really good at computers (as you can see below) but I'll try my best.

The problems I've been having are really simple. Blue Screens, constant freezes, lag, computer would turn on for about 5-10 minutes and then Blue Screen either for a Kernel Error, or a process crucial to the system has stopped working, a message saying "Intel UNDI PXE-2.0 (Build 083)...Check Cable connection...no bootable device". Today, I woke up with it not "working"(the eyes weren't blinking) at the Windows Logo when I was restarting the computer, and then got a blue screen right after that saying PROCESS1_Initialization_ Failed and not being able to do the minidump (error 0x010 or something like that)

Oh, and every time I tried to log on my old account, it froze, and then blue screens. At that time it would lag and freeze for a little bit, but it Blue Screened only once. I'm not sure if I triggered it, since I copied all the files over, and when I ran PC Doctor a few days ago (when I could actually get through sometimes), it told me there was a problem with some files, something that I really didn't understand.

I took a bunch of pictures at the blue screens and some videos of it. I'd be more than happy to share. I've also noticed that, if I got through and logged on my "Guest" account, it wouldn't Blue Screen at all, even when I switched accounts to my newest one. At the Scan I did with PC Doctor a few days ago, it would always fail at the "Test di lettura Mirato" (I bought my computer from Dell Italy), which means Aimed Lecture Test (or something like that), and would Blue Screen with the Process crucial to the system <ADMIN NOTE: Profane word removed per TOU policy>. Like I said before, I have videos on these events if anyone would like to see all of the additional errors.

I'm not sure if all of these problems are related, and I know it's quite a big load to go through. I do appreciate any help offered.

Thank you very much. My last question would be if the HDD is the only source of all my problems. Would replacing it fix about everything? Also, do you recommend any HDDs? I've checked the Dell website, but I'm not sure if I need to look for a really specific one, or just one that would suit my Alienware. Thanks!